Near-Infrared Plasmonic 2D Semimetals for Applications in Communication and Biology

Localized surface plasmon resonance (LSPR) has many applications which require meeting specific wavelength windows. The most prominent examples are photothermal therapy in biology, matched to the biological window (650-1350 nm), and communication relying on photodetection in optoelectronics, matched to the communication window (1260-1675 nm). However, for the classic noble metals (Au, Ag), tuning LSPRs from visible region to these two windows is still a demanding task due to their intrinsic limitations on charge density and dielectric function. Here, the discovery of near-infrared biological and communication window-matched plasmonic properties of semimetal TiS2 nanosheets (NSs) is reported for the first time. Developed synthesis procedures allow fine-tuning width and thickness of single-crystal TiS2 NSs. During characterization a new and intensive absorption peak in the 1000-1400 nm range is observed from both TiS2 NS colloid solutions and films. This peak is attributed to LSPR due to its dependence on particle shape and on the refractive index of solvents. The superiority of such LSPRs is demonstrated in both, biological and optical applications: excitation at 808 and 980 nm generates a similar to 50 degrees C photothermal temperature rise, while excitation at 1310 nm results in two-times enhanced photocurrents of PbS photodetectors compared to untreated devices.